1. Field of the Invention
The present invention relates, in general, to combustible fuel slurries containing liquid hydrocarbon fuel and particulate carbonaceous material, and more particularly, relates to the control of the viscosity of, the settling of particles from, and the prevention of the formation of gels in such slurries.
2. Description of the Prior Art
The possibility of adding solid particulate carbonaceous material, such as coal, to a liquid hydrocarbon fuel, such as fuel oil, has been studied for many years. In the last 3 years, and particularly during the last year, the importance of reducing the dependency of the world upon natural gas and liquid hydrocarbon fuels for its energy has been dramatically demonstrated.
While not constituting a complete solution to this problem, attempts have been made to add solid particulate carbonaceous material, such as coal, to liquid hydrocarbon fuels, because such particulate carbonaceous materials are known to be far more plentiful than liquid fuels. Accordingly, there is considerable renewed interest in the possibility of extending and/or supplementing liquid fuels with solid fuels.
Most heavy industrial fuel users have equipment which is designed and constructed for the transportation, storage and combustion of liquid fuels, and yet prior solid-liquid slurries, suspensions or emulsions have not been accepted for regular use in conventional equipment. In some instances such equipment has been converted from its original design for burning solid fuels, a trend which many now believe may need to be reversed.
Numerous approaches have been taken to the problem of combining a solid particulate carbonaceous material with a liquid hydrocarbon fuel. One approach is simply to grind the carbonaceous material to colloidal size before introducing it into an oil. This is successful, but the grinding cost involved is prohibitive. It was also soon discovered that oil-coal slurries tended to form gels when heated to usable temperatures upon storage, usually thixotropic gels, which were undesirable as such gels interfered with pumping and burning of the slurries.
Attempts were made, however, to use the gelling phenomenon to hold larger than colloidal size particles in suspension. In U.S. Pat. No. 2,423,913, a gel is formed by holding the heated material for over 90 hours. The gel is then broken down with more oil, with the resulting slurry assertedly being pumpable without the particulate material settling out. This is inherently a very expensive batch process. In U.S. Pat. No. 1,684,125 a soap is added to the oil component in sufficient quantities to form a gel, and the particulate material is then added to the gel, with the gel reportedly being used to prevent settling of the particulate material.
Various materials have also been added to attempt to stabilize the slurry against the settling of the larger than colloidal size particles. In U.S. Pat. No. 2,118,477 starch was employed in an attempt to stabilize the slurry, and in U.S. Pat. No. 1,447,008 coal distillates and lime-rosin are used to prevent settling of the larger slurry particles. Casein, gelatin and rubber have also been employed as suspension stabilizing agents to prevent slurry settling. It has been found, however, that such suspension stabilizing agents must be employed in quantities which undesirably thicken and increase the viscosity of the slurry in order to maintain substantial quantities of particulate material from settling from the slurry. Increasing the slurry viscosity does reduce the settling problem, but is also undesirably decreases the number of uses to which the slurry may be put.
Other attempts to stabilize oil-coal slurries have included the use of cracked fuel oils (U.S. Pat. No. 1,939,587) and the use of a substantial percentage of colloidal size particles to stabilize the non-colloidal size particles (U.S. Pat. NO. 2,590,733).
Finally, aqueous stabilized oil-coal slurries have been evolved for pipeline transportation purposes such as is shown in U.S. Pat. No. 3,210,168. Such slurries, however, achieve a desired low slurry viscosity by the addition of substantial amounts of water which undesirably reduces the BTU value of the slurry. Furthermore, the water content of the slurry can be corrosive to the equipment employed in connection with handling and burning the same.
Accordingly, it is an object of the present invention to provide a combustible fuel slurry in which liquid hydrocarbon fuels are extended by solid carbonaceous particles with the resulting slurry being usable in conventional fuel oil transportation, storage and burning equipment.
It is a further object of the present invention to provide a method for controlling the formation of gels in slurries of liquid hydrocarbons and solid particulate carbonaceous materials and to further control, without the use of water, the viscosity of such slurries.
It is still a further object of the present invention to provide a method for stabilizing the settling of larger particles from the slurry without undesirably increasing the viscosity of the same or creating a gel in the slurry or its components.
Another object of the present invention is to create a new, stable, combustible fuel slurry which will provide energy at a cost competitive with or lower than the cost of energy provided by liquid hydrocarbon fuels.
Still a further object of the present invention is to provide a stable, combustible fuel slurry in which the method of forming the same and constituents are relatively easy and inexpensive.
The present invention has other objects and features of advantage, some of which will become more apparent from and are set forth in detail in the accompanying description hereinafter.